1. Field of the Invention
This invention relates to a catalytic converter for purifying exhaust gas discharged from an internal combustion engine for an automotive vehicle, and more particularly to improvements in the catalytic converter having a honeycomb monolithic catalytic element whose catalyst carrier is formed of metallic sheets.
2. Description of the Prior Art
A variety of catalytic converters for purifying exhaust gas from automotive engines have been proposed and put into practical use. One of them is disclosed in Japanese Patent Provisional Publication No. 54-13462 and will be discussed with reference to FIGS. 7A and 7B. A catalytic converter shown in FIGS. 7A and 7B includes a casing 54 disposed in an exhaust pipe of an engine and houses therein a honeycomb monolithic catalyst 51 whose carrier is formed of metallic sheets. The carrier is formed by spirally winding a flat metallic sheet 52 and a corrugated Metallic sheet 53 upon putting one upon another. The thus formed carrier of the honeycomb type carries or supports catalyst on the surface of the metallic sheets 52, 53, thereby forming a plurality of gas passages 51a. The honeycomb monolithic catalyst 51 is tightly disposed in the casing 54 in such a manner that the outer peripheral surface of the catalyst 51 is in contact with the Inner peripheral surface of the casing 54. Exhaust gas from the engine is introduced into the honeycomb monolithic catalyst 51 to pass through the gas passages 51a, so that hydrocarbon, carbon monoxide and the like are oxidized to purify exhaust gas from the engine.
However, difficulties have been encountered in the thus configurated catalytic converter in which the outer peripheral surface 51b of the honeycomb monolithic catalyst 51 is in sliding contact with the inner peripheral surface 54c of the casing 54 during assembly of the catalytic converter and under vibration due to vehicle operation, so that catalyst on the outer peripheral surface of the catalyst is peeled off and scattered to ambient air. Additionally, transmission of reaction heat generated in the catalyst 51 to the casing 54 is suppressed under existence of the layer of the catalyst in contact with the inner peripheral surface of the casing. Accordingly, the honeycomb monolithic catalyst tends to rise in temperature, thereby deteriorating the durability of the catalyst.